Halogen containing-polymer nanocomposite compositions, methods, and products employing such compositions

ABSTRACT

The disclosure provides compositions prepared by combining nanomaterials with a halide-containing polymer, thereby forming a combined polymer matrix having dispersed nanomaterials within the matrix. The nanomaterials may be carbon-based nanotubes, in some applications. A halide-containing monomer is combined with nanotubes, and then polymerized in some compositions. In other applications, a halide-containing polymer is solution processed with nanotubes to form useful compositions in the invention. Also disclosed are probes for near field detection of radiation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 10/103,562 filed on Mar. 21, 2002, now U.S. Pat.No. 7,265,174 which claims priority to an earlier filed provisionalapplication, Ser. No. 60/278,015, filed in the United States on Mar. 22,2001.

FIELD OF THE INVENTION

The invention is directed to uniquely homogeneous dispersions ofnanometer-sized materials in halogen-containing polymers.

BACKGROUND OF THE INVENTION

To materials engineers, composites offer the ability to alter theproperties of materials by combining the functionalities of severalcomponents for a specific purpose. It is widely believed that, forexample, ceramic/polymer nano-engineered composites can be designed toexhibit the overriding strength, dimensional, and thermal stability ofceramics with the fracture properties, processability, and dielectricproperties of polymers. “Matrix Nanocomposites” are a new class ofmaterials, which exhibit ultra-fine dispersed phase dimensions,typically in the 1-100 nm range as well as a physically distinct host orcontinuous phase over much longer average length scales. The nano-lengthscale is the range where phenomena associated with atomic and molecularinteractions strongly influence the macroscopic properties of materialssuch as electrical and thermal conductivity, strength, and opticalclarity, for example, the longer length scale phase are typicallyused—in addition to the afore mentioned macroscopic properties—todetermine processing and fabrication of the composite.

Preliminary experimental work on nano-composite materials have suggestedthat many types and classes of nanocomposites have new and improvedproperties when compared with their macro-scale counterparts (see forexample: Ajayan, P. M. Chem. Rev. 1999, 99, 1787). A predominant featureof these materials is their ultra fine phase dimension and hence surfacearea; therefore a large fraction of the atoms reside at an interface.The properties can therefore be expected to be strongly influenced bythe nature of the interface. For example, a strong interface shouldallow unusual mechanical properties. Since the interface structure playsa critical role in determining the properties of these materials theyare frequently referred to as “interface composites”.

To make a successful nanocomposite it is very important to be able todisperse the secondary phase (be it a nanosized metal, ceramic, orpolymer) throughout the host material and create those interfaces.

Nanocomposites are now becoming viable commercial products. BIB.: Y.Feng, Y. Ou, Y. Zhongzhen, J. Appl. Polym. Sci., 69(2), 355, 1998.).Most research and development is focused on automotive parts andpackaging, and space durable composites (“Fluoropolymer NanotubeComposites for Coatings and Nanoscopic Probes” Shah, H.; Czerw, R.;Carroll, D.; Goldner, L.; Hwang, J.; Ballato, J.; Smith, Jr., D. W.Polym. Mat. Sci. & Eng. (Am. Chem. Soc., Div. PMSE) 2000, 82, 300.),display applications (P. M. Ajayan, O, Stephan, C. Colliex, and D.Trauth, Science, 265, 1212, 1994.), and atomic force microscopy (AFM)probes (Dai, H.; Hafner, J. H.; Rinzler, A. G.; Colbert, D. T.; SmalleyR. E. Nature, 1996, 384, 147 and Hafner, H. G.; Cheung, C.; Lieber, C.M. Nature, 1999, 398, 761).

The benefits of such nanocomposites that have already been identifiedinclude: efficient reinforcement with minimal loss of ductility,improved impact strength, heat stability and flame resistance, improvedgas barrier properties, improved abrasion resistance, reduced shrinkageand residual stress, altered electronic and optical properties (See forexample: “Handbook of Nanophase Materials” A. N. Goldstein, Ed., MarcelDekker, Inc., New York, 1997 and S. J Komarnemi, Mater. Chem., 2, 1219,1992). The shapes of the particles used in nanocomposites can vary fromspherical, fibrilar, to platelets, and each will result in differentproperties modifications to the host. For example: for maximumreinforcement, platelets or fibrilar particles would be used, sincereinforcement efficiency tends to scale with the aspect ratio (L/d).Further, performance benefits of nanoparticulate fillers are availablewithout increasing the density or reducing light transmission propertiesof the base polymer. Although many research projects have been reportedconcerning all types of nanoparticles, the most extensive research hasbeen performed with layered silicates, which provides plateletreinforcement.

Matrix nanocomposites, based on polymers, have been a central area ofpolymer research in recent years and significant progress has been madein the formation of various types of polymer-nanocomposites. Thisincludes an understanding of the basic principles that determine theiroptical, electronic and magnetic properties. An early polymernanocomposite that was developed was the polyamide 6 (from caprolactam),which has dispersed ion-exchanged montmorillonite, a smectic clay, asthe reinforcement. Such nanocomposites typically contain 2-10% loadingson a weight basis, yet property improvements can equal and sometimesexceed traditional polymer composites even containing 20-35% mineral orglass. Machine wear is reduced and processability is better. Becausepolymers are, typically, about one-half as density as mineral and glassfillers these composites offer attractive opportunities for weightsensitive applications, such as auto parts.

Fluoropolymers are known to represent viable alternatives to currentoptical materials particularly for the critical next step in opticalcommunications—access level all-optical networks (Modern Fluoropolymers,Scheirs, J., Ed.; Wiley: New York, 1997).

A pending United States patent application, U.S. Ser. No. 09/604,748entitled “Fluoropolymers and Methods of Applying Fluoropolymers inMolding Processes” and assigned to the assignee of the presentapplication is directed to uses of PFCB compounds in molding processesand optical applications.

Other publications have recited various synthesis methods and uses forPFCB and fluoropolymeric compounds. See, i.e. Smith et al,“Perfluorocyclobutyl Liquid Crystalline Fluoropolymers. Synthesis andThermal Cyclopolymerization ofBis(trifluorovinyloxy)-alpha-methylstilbene”, Macromolecules, Volume 33,Number 4, Pages 1126-1128; See also Smith et. al. “Perfluorocyclobutane(PFCB) polyaryl ethers: versatile coatings materials”, Journal ofFluorine Chemistry 4310 (2000) 1-9. There is great potential for thisoptical fluoropolymer to further enhance its properties by using it in ananocomposite where the nanomaterial provides unique interactions withlight.

In regards to electrically conductive polymer composites, work has beendone using carbon black as a second phase to permit conductivity in anotherwise dielectric host. See Foulger, Stephen: “Reduced PercolationThresholds of Immiscible Conductive Blends”, Journal of Polymer SciencePart B: Polymer Physics, Vol. 37, 1899-1910 (1999).

Although carbon black was used in the previous case, many forms ofcarbon exist. For example carbon may be in the form of submicrongraphitic fibrils, sometimes called “vapor grown” carbon fibers. Carbonfibrils are vermicular carbon deposits having diameters less than about1.0 micrometer. They exist in a variety of forms and have been preparedby catalytic decomposition of carbon-containing gases on metal surfaces.

U.S. Pat. No. 4,663,230 discloses cylindrical ordered graphite cores,uncontaminated with pyrolytic carbon. Blending such fibers with polymershas been known to improve the mechanical properties of the resultingblends.

More recently, it has been found that carbon tubes (often termed“nanotubes”) provide a structure with potential for many suchapplications. In particular, the structure of carbon nanotubes makestheir aspect ratio (length/diameter, L/D) comparable to that of longfibers. Typically the aspect ratio of carbon nanotubes is >10,000. Thus,the aspect ratio of carbon nanotubes is generally much greater than thatof conventional short fibers, such as those often made of glass or otherforms of carbon. In addition, nanotubes sometimes may be lighter thanconventional carbon fibers, which may be helpful in some applications.

Currently, carbon nanofibers and carbon nanotubes figure prominentlyamong the organic-host nanocomposite fillers of interest. Vapor growncarbon nanofibers (VGCFs) in thermoplastic matrices have attracted muchinterest as they have potential application as conducting polymers forelectrostatic dissipative coatings. In addition the VGCFs enhance bothstiffness and thermal stability of the matrix. Thermoplastic matricesnoted in recent studies include polypropylene,acrylate-butadiene-styrene, polyethylene, polycarbonate andpolyether-terephthalate. Naturally, the interactions between the fiberand the matrix at the interfacal level are of critical importance to theproperties of the developed composite. The catalytically grown carbonfibers used in these previous studies have outstanding physicalproperties such as high tensile modulus as well as low electricalresistivity and high thermal conductivity (1,950 W/mK). Further, thesenanofibers can be surface-treated to promote different types of bonding.However, electrical and thermal conductivities as well as yieldstrengths and moduli are orders of magnitude larger for carbon nanotubesand one might want to extend these nanocomposites to include nanotubedispersions instead of VGCFs. This is because network formation at thepercolation threshold of nanotubes may be achieved at relatively lowmass concentrations because of their unusually high aspect-ratios.Hence, enhanced electrical and thermal conductivity may be possible inpolymer/nanotube composites without sacrificing, for example, hostoptical clarity or flexibility.

Unfortunately, control over dispersive characteristics is significantlymore difficult for carbon nanotubes. This comes about because, unlikeVGCF, the surfaces of the nanotubes are exceedingly difficult to modifyas they exhibit, primarily, unreactive carbon-carbon bonds.

Efforts have been made to incorporate carbon nanotubes intohydrocarbon-based polymeric materials, but difficulty has beenencountered in providing compositions that perform well. In general, thenumber of carbon nanotubes that must be placed into a polymericcomposition to achieve superior properties is so high that the actualphysical and structural properties of the polymer may be deteriorated bythe presence of the carbon nanotubes. This difficulty may be due to thefact that carbon nanotubes tend to clump and aggregate together (insteadof uniformly dispersing) when placed in many hydrocarbon-based polymericcompositions.

This relatively poor control over the dispersive characteristics hasmade it difficult to employ carbon nanotubes in useful applications. Thesurfaces of such nanotubes may be exceedingly difficult to modify aswell, since nanotubes exhibit primarily unreactive carbon-carbon bonds.

What is needed in the industry is a composition and method of preparinga composition that is capable of employing the useful properties ofnanomaterial structures in a polymer matrix. A composition thatsuccessfully combines nanomaterial structures uniformly dispersed in apolymer matrix would be highly desirable.

SUMMARY OF THE INVENTION

The invention is directed to uniquely homogeneous dispersions ofnanometer sized materials in halogen-containing polymers. Suchcompositions may include the use of nanotubes such as carbon-basednanotubes. Furthermore, nanotubes may be mixed into a halogen-containingpolymer matrix. A halogen-containing monomer and/or polymer forms acompositional matrix with nanotubes. In some applications, ahalogen-containing polymer is combined with nanotubes to achieve arelatively high level of nanotube dispersion. The homogeneity of thedispersion are superior in the invention.

Some specific applications of the invention employ fluoropolymers, whileother specific applications may employ chloropolymers as the hostpolymer. Various products may employ compositions made according to theinvention. These products and applications include: light emittingdevices, nanoscopic probes, thermal management, electrical conductivity,electromagnetic interference, EMI shielding, linear and nonlinear optics(for example optical limiting), polymer actuation, and stealth (whereeach material can be in film, fiber, powder, liquid resin, or solutionform), and others as well. This list is not exhaustive, and certainlyother applications for the compositions exist as well, such as, forexample, “dual function” applications involving multiples of the aboveproperties. In particular, polymer electrical conductivity in additionto optical clarity represents a major need in applications requiringlight transmission and static charge dissipation (e.g., for spacedurable optical film).

A number of factors combine to fuel interest in polymer basednanocomposite technology using clay minerals which include low loadinglevels, transparency, incorporation flexibility, safety, synergies withother additives and low cost. In the past, combinations of clays in suchmaterials have not been compatible with polymers and hence surfacemodified to render them hydrophobic. Polymers such as polyimide, epoxyresin, polystyrene, polycaprolactone, acrylic polymer and polypropylenehave been explored to fabricate polymer nanocomposites using clays whichform the main inorganic nanocomposites.

BRIEF DESCRIPTION OF THE DRAWING

The following Figures illustrate the invention:

FIGS. 1 a-c show photographs of a PFCB composite;

FIGS. 1 d-f show photographs of PVDF, as further discussed herein;

FIGS. 2 a-c include photos of samples of composites of PVDF/HFP, asfurther discussed herein;

FIG. 3 compares the absorption curves from the PFCB materials with thoseof PVDF and PVDF-copolymer nanocomposites;

FIG. 4 shows scattered light at 500 nm from PFCB, PVDF, andPVDF-copolymer;

FIG. 5 is a 1 mm thick film of polymethylmethacrylate (PMMA);

FIG. 6 is a Table showing surface energies and fluorine content for thepolymers featured in the study herein;

FIG. 7 is a graph of wavelength versus absorption, as further discussedherein;

FIG. 8 a shows a drawn PFCB fiber containing carbon nanotubes; and

FIG. 8 b illustrates a probe having a nanocomposite fiber with ananotube protruding from the frontal surface of the probe.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made to the embodiments of the invention, one ormore examples of which are set forth below. Each example is provided byway of explanation of the invention, not as a limitation of theinvention. In fact, it will be apparent to those skilled in the art thatvarious modifications and variations can be made in this inventionwithout departing from the scope or spirit of the invention.

Both organic and inorganic nanomaterials may be combined withhalogen-containing monomers or halogen-containing polymers in thepractice of the invention. Among the inorganic nanomaterials, some maybe based on clays, such as montmorillonite, kaonite, bentonite, mica,talc, silica nanoparticles and the like as further disclosed in Examplesbelow.

“Nanocomposite materials” or “nanocomposites” as used herein shallinclude a class of materials that exhibit ultra-fine phase dimensions,typically in the 1-100 nm range, as well as a physically distinct hostphase existing over much longer average length scales. The nano-lengthscale is the range in which phenomena associated with atomic andmolecular interactions strongly influence the macroscopic properties ofmaterials such as electrical and thermal conductivity. Longer lengthscales may be used to determine processing parameters of the materials.Although the following discussion focuses primarily on polymer/carbonnanotube-based nanocomposites, in general, “nanocomposite materials” and“nanocomposites” as used herein also refers to other nanosized materialssuch as, but not limited to, those comprised of Group III-through-GroupV-elements, transition metal oxides (e.g., vanadium oxide), and others.

Further, in regards to inorganic/polymer nanocomposites there are atleast two types of inorganic layered silicate/polymer nanocomposites,i.e. intercalates and exfoliates, depending upon the organization of thesilicate layers. Intercalates are obtained when polymer is locatedbetween the silicate layers and while the layer spacing is increased.There are attractive forces between the silicate layers which cause thelayers to be provided in regularly spaced stacks. Exfoliates areobtained when the layer spacing increases to the point at which there nolonger is sufficient attraction between the silicate layers to cause auniform layer spacing. In exfoliates, silicate layers are randomlydispersed throughout the composite.

Organosilicates may be more compatible with engineering plastics, asthey usually contain various functional groups that interact and/orreact with the polymer to improve adhesion between the inorganic phaseand the matrix.

Various methods of synthesis may be employed:

-   -   (1) Nanomaterials can be solution mixed with dissolved        pre-formed polymer.    -   (2) Nanomaterials can be melt mixed with molten pre-formed        polymer.    -   (3) Nanomaterials can be solution mixed with insitu solution        polymerization of the host polymer.    -   (4) Nanomaterials can be melt mixed with insitu melt        polymerization of host polymer.    -   (5) Nanomaterials can be mixed via multi-phase processes        involving both pre-formed polymer and/or insitu polymerization        such as, aqueous dispersion or emulsion polymerization with or        without the addition of surfactants.    -   (6) Nanomaterials can be mixed with pre-formed polymers or by        insitu polymerization as described in 1-5 above with or without        the aid of heat and sonication.    -   (7) Nanomaterials can be mixed with sol-gel precursors such as        tetraalkoxysilanes (e.g., TEOS or TMOS) or otherwise organic        functional trialkoxysilanes and polymerized by catalytic        hydrolysis to a silicate or silicate/organic hybrid        nanocomposite.

Carbon nanotubes are one type of nanomaterial (single-walled ormulti-walled) that sometimes behave like one dimensional metallicconductors or low band gap semi-conductors. Incorporation of carbonnanotubes in insulating polymer matrices may increase the electricalconductivity of the composites by several orders of magnitude. Forpurposes of this specification the term “nanotube” shall refer to ananomaterial that assumes a tubular or cylindrical shape.

Carbon nanotubes may act as nanometric heat sinks. Network formation orpercolation threshold of nanotubes may be achieved at relatively lowconcentrations because of their unusually high aspect ratios. Hence,enhanced electrical and thermal conductivity may be obtained inpolymer/nanotube composites, without sacrificing optical clarity, sincetheir diameter is sufficiently small that light is not strongly absorbedor scattered.

It is advantageous in many industries (including electronics,optoelectronics, and aerospace) to have mechanically flexibleelectrically and thermally conductive coatings and substrates. Inaddition, composites possessing these features and optical clarity aredesired. In the present invention, the halopolymer nanocompositespossess the requisite thermal and electrical conductivities. Morespecifically, for aerospace structures, a conductivity of ca. 10-⁷ S/cmis needed for static charge dissipation. Further, management of thermalcycles on aerospace structures also is desired. The halopolymernanocomposites exhibit adequate thermal and electrical conductivity forthese applications while maintaining mechanical flexibility andtoughness as well as optical clarity. This is realized through theunique level of dispersion for very low loadings (<0.1 to 5 weight %) ofhigh conductivity nanotubes afforded by the halopolymer host comprisedin the nanocomposites disclosed in the invention.

It has been found that halogen-containing polymers exhibit uniquecompatibility with carbon nanotubes, and that such nanotubes may bedispersed by simple solution or melt processes to provide unique levelsof homogeneity. In this invention, the dispersion properties of carbonnanotubes are disclosed for several halogen-containing polymer matrixformations.

In making the compositions of the invention, it is possible to combinenanotubes with halogen-containing monomers. It also is possible tocombine nanotubes with halogen-containing polymers. That is,polymerization may occur either before or after application ofnanotubes, depending upon the particular application. Copolymers alsomay be used.

The invention is comprised, in one embodiment, of a composition preparedby combining nanomaterials with a halogen-containing polymer or monomerto form a nanocomposite. In one application of the invention, carbonnanotubes may be dispersed in a halogen-containing polymer by melt orsolution processing to form a nanocomposite. Furthermore, at lownanotube loading levels, the resulting composition may be formed into atransparent film, fiber, powder, liquid resin, or solution.

A “halogen-containing polymer” or “halogen-containing monomer” asdescribed herein and as employed in the invention may includeessentially any or all Group VII elements within a polymeric structure.The halogen species may be fluorine, chlorine, bromine or iodine, forexample, depending upon the particular application.

In one specific aspect of the invention, the halogen-containing polymercomprises a fluoropolymer such as those derived from monomers containingtrifluorovinyl ether (TFVE) groups (as initially described in:“Fluoropolymer Nanotube Composites for Coatings and Nanoscopic Probes”Shah, H.; Czerw, R.; Carroll, D.; Goldner, L.; Hwang, J.; Ballato, J.;Smith, Jr., D. W. Polym. Mat. Sci. & Eng. (Am. Chem. Soc., Div. PMSE)2000, 82, 300).

Whereas these polymers are receiving consideration for structuralcomposites, there are commercial applications of equal importance foroptical composites. From a potential host materials perspective,perfluorocyclobutane (PFCB) polymers have suggested for use in opticalfibers and dielectric waveguides. See, for example, “Property TunablePerfluorocyclobutyl (PFCB) Copolymers for Optical Devices” Smith, Jr.,D. W.; Kumar, S.; Chen, S.; Ballato, J.; Nelson, E.; Jin, J.; Foulger,S. in Design, Manufacturing, and Testing of Planar Optical WaveguideDevices, R. A. Norwood, Ed. SPIE Proc. 2001, 4439, 51-62.

In specific applications, the fluoropolymer may comprise aperfluorocyclobutane (PFCB) aromatic ether moiety, as further discussedherein. In still other applications, other halogen-containing polymersor monomers or copolymers may be employed, including copolymers of PFCB,polyvinylidenedifluoride (PVDF), and copolymers of PVDF.

Other fluoropolymers and chloropolymers that may be employed includethose polymers and copolymers made from monomers such as: perfluoroallylvinyl ethers, chlorotrifluoroethylene, fluorovinyl ethers,hexafluoroisobutylene, hexafluoropropylene, hexafluoropropylene oxide,perfluorormethyl vinyl ether, perfluoroalkyl vinyl ether,fluoroalkylacrylates, fluoroalkylmethacrylates, tetrafluoroethylene,vinylidene dichloride, vinyl fluoride, vinylidene difluoride,trifluoroethylene, and vinyl chloride. Some commercial trade names forfluoropolymers which may be employed include: Teflon, Teflon AF, Cytop,Halar, Tefzel, Hostaflon ET, Aflon COP, Neoflon, Teflon FEP, HostaflonTFA, Algoflon, Neoflon AP, Kel-F, Aclon, Voltaflef, Diaflon, Teflon PFA,Fomblin, Krytox, Denum, Teflon PTFE, Fluon, Hostflon PTFE, polyflon,Kynar, Hylar, Solef, KF, Tedlar, Viton A, Flurel, Technoflon, Dai-el,THV, Fluorobase T, Viton B, Kelrez, Aflas, Kel-F 3700, Technoflon XL,Technoflon G, Viton G, Viton GLT.

Other halogenated polymers that may be employed include: halosilicones,halopolyurethanes, halopolyphosphazenes, halopolycarbonates, haloepoxyresins, halopolyamides, halopolyimides, halocyanurate resins,halopolystyrenics, halogenated polyolefins, halopolycyclohexane,halogenated ethylene-propylene-dienemonomer (EPDM) resins, halogenatedacrylics, and halogenated polyacrylonitriles.

EXAMPLES

The host materials used in this study are a set of four fluoropolymerswith different atomic percentages of fluorine. The polymers, describedin some detail below, are a perfluorocyclobutyl (PFCB) aromaticpolyether thermoplastic, one copolymer of PFCB, andpoly(vinylidenedifluoride) (PVDF) and one copolymer of PVDF. These arecompared to a limited extent with poly methylmethacrylate (PMMA).

Host Materials PFCB/PFCB-Copolymer

Perfluorocyclobutyl (PFCB) polymers used were prepared from commerciallyavailable precursors as described elsewhere. Specifically, thermoplasticPFCB polymers used in this study were prepared from4,4′-bis(trifluorovinyloxy)biphenyl or4,4′-bis(trifluorovinyloxyphenyl)hexafluoro-isopropylidene, or forcopolymers, a trifunctional comonomertris(trifluorovinyloxyphenyl)ethane.

Perfluorocyclobutyl (PFCB) polymers are prepared from the free radicalmediated thermal cyclopolymerization of trifunctional and bifunctionalaryl trifluorovinyl ether monomers from which a variety of thermallystable (T_(g)˜350° C.), low dielectric constant thermoplastic andthermosetting materials can be obtained. As a unique class of partiallyfluorinated polymers, PFCB polyaryl ethers combine the processabilityand durability of engineering thermoplastics with the optical,electrical, thermal, and chemical resistant properties of traditionalfluoroplastics. This makes them particularly interesting fornanocomposite work.

To create the initial nanocomposite matrix, trifunctional monomer1,1,1-tris-(4-trifluorovinyloxyphenyl)ethane was used. Since thismonomer has a melting point just above room temperature (40 C), MWNTswere easily mixed with the liquid monomer by ultra-sonication for 1hour. After sonication, the monomer/MWNT solution was a grayish,translucent liquid with very little visible aggregation. The solutionwas then polymerized by thermal cyclo-polymerization. The resultingnanocomposite as can be seen in FIG. 1 b.

Host Materials PVDF/PVDF-Copolymer

The second major class of fluoropolymers used in this study,Polyvinylidene difluoride (PVDF), possesses a unique blend of propertiesthat makes it amenable to many processing techniques and many end uses;particularly its piezoelectricity is widely utilized commercially.

PVDF is a crystalline polymer (mp.=171° C.). Since thepoly(vinylidenedifluoride) for the work is commercially availablepolymerization routes and synthesis chemistry will not be discussed herein detail. The copolymer of PVDF,Poly(vinylidenedifluoride-co-hexafluoropropylene) (HFP), is the othercopolymer examined in this study and is generally prepared by emulsionpolymerization under pressure using a persulfate-bisulphite initiationsystem for free radical polymerization. The PVDF itself is highlycrystalline. When copolymerized with hexafluorpropylene (HFP), thedegree of crystallinity is greatly reduced and its solubility insolvents is increased.

The PVDF and HFP were dissolved in N,N-dimethylacetamide (purchased fromAldrich Chemical) to give a 10% solution by weight. Occasional stirringwas done to promote dissolution. To these polymer solutions weighedproportions of purified MWNTs were added and sonicated in a water bathfor close to 3 hrs. The sonicated solutions look gray-black in color andare further sonicated in a probe type sonicator (Branson Sonifier) forapproximately 30 mins. The high power ultrasonication enhances theextent of mixing, which results in the presence of very little visibleaggregation.

The sonicated samples were drop cast on silicon wafers heated to 120° C.Resulting films are approximately 70-80 microns thick, with no visibleaggregates. For thicker samples (˜100-120 microns), films were cast in aTeflon mold. The MWNT loading used varied for different propertyanalysis ranging from 0.1-35 wt %.

The molecular weights of the polymers used for these studies wereapproximately 50,000 for the PFCB thermoplastic and pre-network resins;and around 500,000 for the PVDFs. As noted, the PVDF tends to be rathercrystalline in morphology, whereas the PFCB/PFCB-co and PVDF-co exhibita glassy microstructure. Volume resistivity data was collected using aKeithley 8009 Resistivity Test Fixture and Keithley Electrometer (ASTMD257).

In some applications, a composition is made having carbon-basednanotubes or nanomaterials showing a thermal conductivity greater than1.25 W/mK at a nanomaterial loading level of about 0.01 to about 10weight %. In other applications, the composition may show a volumeresistivity of less than about 10¹⁰ ohm cm at a nanomaterial loadinglevel from about 0.01 to about 10 weight %. Furthermore, in otherapplications a composition may exhibit an optical transmission ofgreater than 80% at a nanomaterial loading level of about 0.01 to about80 weight %. In yet other applications, the composition may show anoptical transmission of greater than 50% at a nanomaterial loading levelfrom about 0.01 to about 5 weight %.

Microscopy

To first examine the microstructure of the matrix nanocomposites, weimaged fracture surfaces of the materials with a field-emission SEM(Hitachi 4700S). Shown in FIG. 1 is a series images fluoropolymernanocomposites loaded with 1% wt. of MWNTs (multiwalled carbonnanotubes). The nanophase of the composites in this study are all arcgrown MWNTs with diameters ranging from 5 nm to 30 nm and generallyaround 1 micron in length. FIGS. 1 a, b, c, show a PFCB composite. FromFIG. 1 a, it is clear that settling occurs during processing. In fact,for the PFCB hosts, the nanomaterials are always observed settled to thebottom surface of the films. For thinner films as used in the opticalstudies of this work, this effect is minimized. FIG. 1 b does show,however, that the volume of the settled material is infused with polymerand nanotubes. When the edges of the settled regions are examined (FIG.1 c) it is clear that the nanotubes are in small bundles and thatagglomeration has been well mitigated.

Agglomerate mitigation is also observed for the PVDF composites. Noticethat while most of the nanocomposite for the 1% wt. loaded PVDF hostappears extremely uniform (FIG. 1 d), occasional agglomeration of thenanophase is observed as in FIG. 1 e. Naturally, it is important torealize that for the PVDF hosts used, a much higher molecular weight ofthe polymer is being processed than in the case of the PFCBs. This leadsto higher viscosities and higher processing temperatures with the resultthat initial blends are not as complete. However, these largeagglomerates are not extremely common within the host and generally mostof the nanomaterials have been effectively incorporated into the matrix.

As a demonstration of the overall clarity of the nanocomposites, FIG. 1f shows an optical micrograph of a PFCB matrix nanocomposite loaded to0.5% wt. This photograph is looking through the 1 mm thick composite at12 point type letters from a laser printer. The dots around thelettering are due to overspray of the printer. No aggregation ofagglomeration can be seen for these large samples and the opticaltransmission of this particular example is approaching 80%.

In FIGS. 2 a-f, the separation of nanotube bundles into isolated tubesis examined using both SEM and TEM (scanning electron microscopy andtransition electron microscopy). In FIG. 2 a, the bundles exiting thePFCB hosts indicate that tube separation is incomplete but sufficientstill that the samples are optically clear (at low tube loadings). FromTEM, FIG. 2 b, c, a number of isolated individual nanotubes can be seenthroughout the matrix. These nanocomposites are formed withoutsignificant shear forces being added during matrix processing. Thus,nanotube separation from bundles is primarily due to wettinginteractions with the host.

Optical Scattering

While electron and optical microscopy is one way of determining localdispersion characteristics, it is instructive to look at averagedispersion properties over large areas. Optical scattering is a quickand easy way to understand the average particle size within the matrix.Though we will not present quantitative light scattering numbers here acomparison of the scattering for samples of the same thickness shows aninteresting trend. FIG. 3 compares the absorption curves from the PFCBmaterials with those of the PVDF and PVDF-co nanocomposites. These filmswere 1 mm thick and the curves were taken using a Perkin ElmerLambda-900 UV-Vis-NIR spectrometer. Notice in each case the strongRayleigh component of the scattering. As is well known in optics ofscattering media, this short wavelength tail is directly related to thesize of the scattering particles assuming small host influences and asmoothly varying function of reflectivity and absorption. For the caseof carbon nanotubes (multiwalled) these Rayleigh tails should bedirectly proportional to the aggregate size within the matrix. Clearly,the Rayleigh scattering has been strongly suppressed in all of thefluoropolymer composites. However, the PVDFs exhibit a strongersuppression of this scattering than does the PFCB. In fact, thePVDF-copolymer has the smallest Rayleigh scattering of any of thecomposites. If the light scattering at a given wavelength is comparedbetween the different hosts, we can see that the increase in Rayleighscattering (as a function of loading from 0.1% to 1.0%) is the strongestwith the PFCBs and weaker for the PVDF-copolymer. In the example of FIG.4, we examine the total scattered light at 500 nm from PFCB, PVDF,PVDF-copolymer. The loading in each of these hosts increases, the totalscattered light from PFCB and PVDF composites is more than double thatof PVDF-copolymer composites for the same incident flux at loadingsabove 0.5% wt. Since the Rayleigh component of the scatter is, by far,the largest component of this scattered light, we interpret this asmeaning that the size of the aggregates within the matrices is smallerfor the PVDF-copolymer composites and is larger for the PVDF and PFCBcomposites. Further, as expected, this aggregation grows with theloading.

Results

To understand these results in context, a comparison with opticallytransparent, nonfluorinated polymers is useful. Shown in FIG. 5 is a 1mm thick film of polymethylmethacrylate (PMMA). Large aggregates can beseen. These composites were created in an analogous fashion to thefluoropolymer examples discussed herein. The PMMA was solved in acetoneand mixed with a suspension of MWNT, also in acetone.

Generally, microscopy and optical scattering suggests that the fluorinecontent of the polymers is responsible for the dispersioncharacteristics. In FIG. 6, surface energies and fluorine content iscompared for the five polymers used in this study. The estimate ofdispersion quality is, of course, subjective and based on bothmicroscopy as well as optical scatter. The surface energies in thisstudy were determined using a contact angle meter and Fowke'stwo-component model. These numbers correlate well with the suppliers forPVDF and PMMA. Notice that the surface energy is roughly the same in thecase of PFCB and PMMA yet the dispersion is significantly better in thecase of the fluoropolymers. Though the PFCB has a higher surface energythan that of the PVDF (PVDF-copolymer was not determined), thedispersion quality seems to scale directly with fluorine content.

Recently there have been several works discussing fluorine doping ofcarbon nanotubes. This suggests strong interactions between nanotubesand fluorine and suggests this as the mitigating factor in theinter-tube van der Waals interactions. This, too, suggests that equallyas reactive chloro-polymers might make equally as good host materials.As an initial investigation, Poly vinyl chloride was used as a host andblended with MWNTs in an analogous fashion to the composites above. FIG.7 shows the optical scattering from PVC-nanotube composites for 1% wt.loading and 0% loading. Surprisingly, these host materials show verylittle Rayleigh scattering. This, again, supports the general idea thatthe halocarbon nature of the host polymer can be used to disperse thenanotubes using low-shear blending methods.

It has been demonstrated in these examples that a new class offluorocarbon matrix composites may be employed based on carbon nanotubesdispersed in fluoropolymer hosts. Clearly, other halo-polymers alsocould be used, with varying results depending upon the particularpolymer selected, and the manufacturing and processing conditions.Different applications may use other types of halo-polymers, stillwithin the scope of this invention.

Optical scatter and microscopy data suggests that dispersion can bedirectly controlled by adjusting the fluorine content of the polymer.Further, the role of the fluorine is mitigation of tube-tubeinteractions to allow for low-shear blending. These composites provideopportunities in the creation of new optically transparent, for example,and potentially electrically conductive films and the potential for newnonlinear optical materials.

In another application of the invention, the nanocomposite is employedas the sensing probe in atomic force and near field optical microscopes.The probe may employ a frontal face having a nanotube protrudingtherefrom as the sensing element. As an example, a carbon nanotubecomposite of the invention has the potential to dramatically improvespatial resolution of these scanning probe microscopes.

FIG. 8 a shows a drawn PFCB fiber containing carbon nanotubes. FIG. 8 bprovides a micrograph of a near field optical probe using a frontalsurface. In FIG. 8 b, a near field optical probe 9 shows dispersednanotubes 10. For example, the nanotube 10 shown may in someapplications be approximately 0.4 μm from tip to tip. Furthermore, afiber frontal surface 11 is shown which corresponds to the ending pointfor one tip of the nanotube 10. The field of view 12 (of the probe 9) isshown beyond the fiber frontal surface 11. The field of view 12 is thearea under examination by probe 9.

As provided below, the compositions of the invention exhibit adequatethermal and electrical conductivity for these applications whilemaintaining mechanical flexibility, toughness, and, potentially, opticalclarity. This is realized through the unique level of dispersion forvery low loadings (<0.1 to 5 weight %) of high conductivity nanotubes ina halopolymer host.

PFCB chemistry is generally well suited for carbon nanotube compositefabrication. Carbon nanotubes can be easily and uniformly dispersed intrifluorovinyl ether (TFVE) monomers by gentle sonication at ca. 70° C.Multi-walled and single walled nanotubes could be employed. Bulkpolymerization of the mixtures results in optically clear nanocompositesat low loading levels. It is possible to fabricate nanocompositescontaining isolated carbon nanotubes in fluoropolymers for bothspecialty coatings and nanoprobe applications. Very low levels ofwell-dispersed nanotubes may be used in coatings which requiremultifunctional properties.

In the practice of the invention, it is possible to provide ahalogen-containing polymer with carbon nanotubes, and to form a combinedpolymer matrix of dispersed carbon nanotubes within the polymer matrix.There is no limit to the number of halogen-containing polymers that canbe used in the practice of the invention. For example, polymerscontaining bromine, chlorine, iodine and fluorine are examples ofhalogens which can be incorporated into polymeric structures in thepractice of the invention.

Example Halo-Polymer Compositions with Clay Materials

Nanocomposite matrix compositions may be developed usinghalogen-containing monomers or polymers or co-polymers as describedabove in connection with the Examples (or other halogen-containingmonomers or polymers as disclosed in this specification) as combinedwith various clay materials. For example, it is possible to provide inthe matrix set forth in the examples above to include a clay product,such as a hydrated aluminum silicate (as one example).

Naturally occurring clays may be used, including but not limited tokaolinite, bentonite, mica, talc, silica nanoparticles, montmorillonite,attapulgite, illite, bentonite, halloysite, fullers earth, kaolin, andpolyorganosilicate graft polymers.

There are numerous applications of the compositions of this invention,and the scope of this invention is not limited to any particularcomposition. It is understood by one of ordinary skill in the art thatthe present discussion is a description of exemplary embodiments only,and is not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstructions. The invention is shown by example in the appended claims.

1. An electrically conductive film comprising: a plurality of singlewalled carbon nanotubes, wherein the film is optically transparent andelectrically conductive, wherein the film has an optical transmissiongreater than 80%.
 2. The film of claim 1, wherein the nanotubes arepresent in the film at about 0.01 to about 5 weight percent.
 3. The filmof claim 1, wherein the film comprises a solid film.
 4. The film ofclaim 1, wherein the film comprises a liquid film.
 5. The film of claim1, further comprising a polymeric material.
 6. The film of claim 5,wherein the polymeric material comprises a polymer matrix containing thecarbon nanotubes.
 7. The film of claim 1, wherein the carbon nanotubescomprise a carbon nanotube network.
 8. The film of claim 1, wherein thefilm is optically clear.
 9. The film of claim 1, wherein the film has avolume resistivity of less than 10¹⁰ ohm cm.
 10. An electricallyconductive film comprising: a plurality of single walled carbonnanotubes, wherein the film has an optical transmission greater than 50%and a volume resistivity of less than 10¹⁰ ohm cm.
 11. The film of claim10, wherein the film has an optical transmission greater than 80%. 12.The film of claim 10, wherein the nanotubes are present in the film atabout 0.01 to about 5 weight percent.
 13. The film of claim 10, whereinthe film comprises a solid film.
 14. The film of claim 10, wherein thefilm comprises a liquid film.
 15. The film of claim 10, furthercomprising a polymeric material.
 16. The film of claim 15, wherein thepolymeric material comprises a polymer matrix containing the carbonnanotubes.
 17. The film of claim 10, wherein the carbon nanotubescomprise a carbon nanotube network.
 18. The film of claim 10, whereinthe film is optically clear.
 19. The film of claim 10, wherein the filmis optically transparent.
 20. An electrically conductive filmcomprising: a plurality of single walled carbon nanotubes, wherein thefilm is optically transparent, optically clear and electricallyconductive, wherein the film has an optical transmission greater than50%.
 21. The film of claim 20, wherein the nanotubes are present in thefilm at about 0.01 to about 5 weight percent.
 22. The film of claim 20,wherein the film comprises a solid film.
 23. The film of claim 20,wherein the film comprises a liquid film.
 24. The film of claim 20,further comprising a polymeric material.
 25. The film of claim 24,wherein the polymeric material comprises a polymer matrix containing thecarbon nanotubes.
 26. The film of claim 20, wherein the carbon nanotubescomprise a carbon nanotube network.
 27. The film of claim 20, whereinthe film has an optical transmission greater than 80% and a volumeresistivity of less than 10¹⁰ ohm cm.
 28. The film of claim 20, whereinthe film has a volume resistivity of less than 10¹⁰ ohm cm.
 29. Adispersion of nanotubes comprising a plurality of single walled carbonnanotubes, wherein when applied to a surface as a film of carbonnanotubes the dispersion has an optical transmission greater than 50%.30. The dispersion of claim 29, wherein the film has an opticaltransmission greater than 50%.
 31. The dispersion of claim 29, whereinthe nanotubes are present in the dispersion at about 0.01 to about 5weight percent.
 32. The dispersion of claim 29, wherein the dispersioncomprises a liquid dispersion.
 33. The dispersion of claim 29, furthercomprising a polymeric material.
 34. The dispersion of claim 33, whereinthe polymeric material comprises a polymer containing solution.
 35. Thedispersion of claim 29, wherein the film has an optical transmissiongreater than 80% and a volume resistivity of less than 10¹⁰ ohm cm. 36.The dispersion of claim 29, wherein the film is optically transparent,optically clear and electrically conductive.